As air traffic increases, many air traffic controllers are issuing required time of arrival (RTA) instructions to aircraft to more tightly control air traffic. For example, an air traffic controller at a particular airport may issue a first RTA to a first aircraft and a second RTA to a second aircraft to control what times the aircraft arrive at a particular location and to prevent the aircraft from arriving concurrently. In situations where no RTA is issued, a flight crew (e.g., a pilot) of an aircraft may enter a cost index into a flight management system, as well as an origin and a destination for a flight and any waypoints along the flight. The flight management system determines a flight plan for the flight from the origin to the destination, including a speed for the flight. The speed is determined based on the cost index value, which indicates a tradeoff between fuel cost (e.g., fuel usage) and cost of manpower and overhead associated with the flight. For example, based on a low cost index value, the flight management system will select a low speed that conserves fuel (e.g., that lowers fuel costs), and based on a high cost index value, the flight management system will select a high speed that reduces a duration of the flight and thereby reduces the costs of manpower and overhead associated with the flight.
When an RTA to a particular location is issued to an aircraft, a pilot of the aircraft enters the RTA into the flight management system (or the flight management system receives the RTA via a datalink). The flight management system determines an RTA speed to enable the aircraft to meet the RTA at the particular location. The RTA speed may differ from the speed associated with the flight plan. After determining the RTA speed, the flight management system controls one or more aircraft controls to set the speed of the aircraft at the RTA speed in order to meet the RTA at the particular location. Because the flight management system determines the RTA speed automatically, the flight crew is unable to control the speed of the aircraft during flight without switching to manual control.